<?php
/**
 * 截取字符串.
 */
function my_substr($str, $start, $length, $charset = 'utf-8', $suffix = true)
{
    $neEFTr = '';
    if (function_exists('mb_substr')) {
        if ($suffix) {
            $neEFTr = mb_substr($str, $start, $length, $charset);
        } else {
            $neEFTr = mb_substr($str, $start, $length, $charset);
        }
    } elseif (function_exists('iconv_substr')) {
        if ($suffix) {
            $neEFTr = iconv_substr($str, $start, $length, $charset);
        } else {
            $neEFTr = iconv_substr($str, $start, $length, $charset);
        }
    }
    if ($neEFTr == '') {
        $re['utf-8'] = "/[\x01-\x7f]|[\xc2-\xdf][\x80-\xbf]|[\xe0-\xef][\x80-\xbf]{2}|[\xf0-\xff][\x80-\xbf]{3}/";
        $re['gb2312'] = "/[\x01-\x7f]|[\xb0-\xf7][\xa0-\xfe]/";
        $re['gbk'] = "/[\x01-\x7f]|[\x81-\xfe][\x40-\xfe]/";
        $re['big5'] = "/[\x01-\x7f]|[\x81-\xfe]([\x40-\x7e]|\xa1-\xfe])/";
        preg_match_all($re[$charset], $str, $match);
        $slice = implode('', array_slice($match[0], $start, $length));
        if ($suffix) {
            $neEFTr = $slice;
        }
    }

    return (strlen($str) > strlen($neEFTr)) ? $neEFTr.'...' : $neEFTr;
}